After death
In Hinduism people believe in samara, when someone dies their body can be reborn in another human being or animal. In English this belief of a body being reborn is called reincarnation. The soul keeps being reborn until is reaches moksha, that is when the soul is united with the god Brahma.
karma
Hindu people believe that a persons Karma will determine how their soul will be reborn in their next life. The definition of karma is actions or deed. For example, if a person does good deeds in their life, that persons soul will be reincarnated into a higher and better form. If a person does bad deeds in their life, that person will be reincarnated into a lower form like into a body of an animal or insect.
caste system
Caste system is a very old practice that was based on Hinduism, it is connected with karma, if one lives a good life full of good deeds, they will be rewarded with the highest level in the Caste System. If you look below there is an image of how the Caste system is structured and what kinds of people it consists of.